High energy rechargeable lithium batteries would be of great importance for the entire field of heart pump development and other implantable or portable medical or biomedical devices, providing energy densities well in excess of what nickel-cadmium batteries deliver at present. Future progress in this area is shown to depend on successful development of a lithium electrode (anode) with desirable rechargeability characteristics. The basic criteria for rechargeability of lithium anodes are discussed as well as anode electrocrystallization. A multicomponent approach to electrolyte design is described in which cosolvent mixing is shown to provide desirable properties as a result of synergistic effects. A strong case for future development of reducible-type cathodes is presented since cathode selection is shown to affect criteria for attainment of desirable electrolytes. Results of the Phase I program are presented. Electrolytes are described which satisfy the criteria for Li cell rechargeability including high specific conductivity to enable high discharge rates, a stable potential window, and a high Coulombie Li stripping efficiency to enable long cycle life.